This invention is generally directed to new toner compositions, and developer materials containing such compositions, as well as the use of such compositions in electrophotographic imaging systems. More specifically, the present invention is directed to toners containing certain charge control additives, which additives impart a positive charge to the toners involved. Toner materials containing such additives are in one embodiment of the present invention useful in electrophotographic imaging systems employing a Viton fuser system, as more specifically detailed hereinafter.
The electrophotographic process and more specifically, the xerographic process is well known, as documented in several prior art references. In these processes, an electrostatic latent image is developed by applying electroscopic particles or toners to the electrostatic image to be developed, using for example cascade development as described in U.S. Pat. No. 3,618,552, magnetic brush development as described in U.S. Pat. Nos. 2,874,063 and 3,251,706, or touchdown development as described in U.S. Pat. No. 3,166,432. In some instances it may be desirable in such systems to produce a reverse copy of the original. Thus, for example, it may be desirable to produce a negative copy from a positive original or a positive copy from a negative original.
It is known in the prior art that certain charge control agents can be used for the purpose of providing a positive charge to the toner material. For example, U.S. Pat. No. 3,893,935 discloses the use of certain quaternary ammonium compounds as charge control agents for electrostatic toner compositions. According to the disclosure of this patent, certain quaternary ammonium compounds when incorporated into toner materials were found to provide a toner composition which exhibited relatively high uniform and stable net toner charge, when mixed with a suitable carrier vehicle. U.S. Pat. No. 4,079,014 contains a similar teaching with the exception that a different charge control agent is used, namely a diazo type material. Further, other charge control agents have been described in Xerox copending applications including for example alkyl pyridinium materials, reference U.S. Ser. No. 911,623, filed on June 1, 1978.
Many of the above charge control agents interact with certain fuser rolls used in electrophotographic systems such as the Viton fuser roll which causes such fusers to be adversely affected and thus cause a deterioration in the image quality. For example, the Viton fuser rolls discolor and turn black, as well as develop multiple surface cracks when certain charge control additive compounds are employed in the toner mixture.
One Viton fuser roll used in electrophotographic copying machines, particularly xerographic copying machines, is comprised of a soft roll fabricated from lead oxide and dePont Viton E-430 resin (a vinylidene fluoride, hexafluoropropylene copolymer). Approximately 15 parts of lead oxide and 100 parts of the Viton E-430 are blended together and cured on a roll at elevated temperatures. Apparently the function of the lead oxide is to generate unsaturation by dehydrofluorination for cross-linking and to provide release mechanisms for the toner. Excellent image quality has been obtained with the use of Viton fuser rolls, however, in some instances there is a toner fuser compatibility problem when charge control agents are part of the toner mixture. It appears that certain charge control additives such as quaternary ammonium compounds and alkyl pyridinium compounds react with the Viton fuser roll. For example, an alkyl pyridinium chloride, such as cetyl pyridinium chloride when part of the toner mixture appears to be catalytically decomposed by the lead oxide in the fuser roll, resulting in a highly unsaturated compound which polymerizes and condenses with the unsaturated Viton. As a result the Viton fuser turns black and develops multiple surface cracks, thereby resulting in image quality deterioration.
Accordingly there is a need for toners, and developers containing such toners, which can be used in a reversal system, and more specifically, there is a need for positively charged toner materials for use in electrophotographic systems employing Viton type fuser rolls, thus allowing the production of high quality images over a long period of time. Further there is a need for toners which will rapidly charge new uncharged toner being added to the developer package, which toners are humidity insensitive, as well as being compatible with Viton fuser rolls.